Diagnosis

Either an ophthalmologist or an optometrist can examine patients for cataracts, but only ophthalmologists are qualified to treat cataracts.

• An ophthalmologist is a doctor who specializes in the medical and surgical care of the eye.
• An optometrist is engaged in the practice of eye care, but is not a doctor and cannot prescribe medication or perform surgery.

The Diagnostic Tests

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The eye professional can observe cloudy areas on the lenses with a direct physical examination, even before the cataracts begin to interfere with vision. Cameras can measure the cataract density. Various vision tests are also performed.

Snellen Eye Chart. To determine how clearly a person can actually see, the Snellen eye chart is used, with rows of letters decreasing in size:

• From a specified distance, usually 20 feet, a person reads the letters using one eye at a time.
• If a person can read down to the small letters on the line marked 20-feet, then vision is 20/20 (normal vision).
• If a person can read only down through the line marked 40-feet, vision is 20/40; that is, from 20 feet the patient can read what someone with normal vision can read from 40 feet.
• If the large letters on the line marked 200-feet cannot be read with the better eye, even with glasses, the patient is considered legally blind.

The visual acuity test can be performed in many different ways. It is a quick way to detect vision problems and is frequently used in schools or for mass screening. Driver license bureaus often use a small device that can test the eyes individually and then together.

Other Tests. There are a number of other tests used to diagnose cataracts or to determine if surgery is needed.  

• A chart similar to the Snellen chart, which has the same size letters, but in different contrasts with background, is used to test contrast sensitivity,
• Glare sensitivity is tested by having the patient read a chart twice, with and without bright lights.
• Tests of macular function, which evaluate the eye's acute vision center, can help the ophthalmologist determine the expected improvement from surgery.
• The corneal endothelium, a layer of cells lining the cornea, is sensitive to surgical trauma and should be evaluated before any intraocular operation.
• Patients with other eye disorders may require a number of other pre-operative tests.

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